DMZ and forwarding ports?

[Brood]

I hope this is going to be my last topic, because damn it I've started a lot in order to get help with setting up a server. It seems everything is wrong with my computer and internet connection: Dynamic IP, router, etc. etc., but now I've finally come down to the last (for the love of God, pleeease!) problem, the router.

To tell you the truth I know nothing about that, nada, completely blank. I don't know what DMZ is, I don't know how to forward ports, and everywhere I search on the forum they seem to just assume you do. So I'm going to ask here, what do I do?! How do I forward a port and enable 7990-8000 and 9000 or whatever I need to use, and what is DMZ? What does it do? What can I use it for? Etc. etc. Help will be very much appreciated, I've spent so many hours trying to get that god damned server to work, and to just be stuck at what seems to be the last problem will be devastating for me.